This application is related to co-filed U.S. patent application Ser. No. 09/292,125, by John D. Rhodes et al. for Vacuum Control for Vacuum Holddown, and U.S. patent application Ser. No. 09/292,838, by Geoff Wotton et al. for a Vacuum Surface for Wet Dye Hard Copy Apparatus.
1. Field of the Invention
The present invention relates generally to a vacuum holddown apparatus and method of operation and, more specifically to a cut-sheet print media vacuum holddown particularly useful for a hard copy apparatus, such as an ink-jet printer.
2. Description of Related Art
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, xe2x80x9cvacuum induced forcexe2x80x9d is also referred to as xe2x80x9cvacuum induced flow,xe2x80x9d xe2x80x9cvacuum flow,xe2x80x9d or more simply as just xe2x80x9cvacuumxe2x80x9d or xe2x80x9csuctionxe2x80x9d.] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum through the drum cylinder provides a suction force at the holes in the drum surface. [The term xe2x80x9cdrumxe2x80x9d as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term xe2x80x9cplatenxe2x80x9d can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, such as a common typewriter rubber roller; thus, for the purposes of the present application, xe2x80x9cplatenxe2x80x9d is used generically for any shape paper holddown surface used in a hard copy apparatus.]
Generally in a hard copy apparatus implementation, the platen is used either to transport cut-sheet print media to a printing station of a hard copy apparatus, such as a copier or a computer printer, or to hold the sheet media at the printing station while images are formed (known as the xe2x80x9cprint ages zonexe2x80x9d), or both. [In order to simplify discussion, the term xe2x80x9cpaperxe2x80x9d is used hereinafter to refer to all types of print media. No limitation on the scope of the invention is intended nor should any be implied.]
One universal problem, particularly pertinent in the adaptation of a vacuum holddown to use in a hard copy apparatus, is the management of different sized paper. Open holes around the edges of a sheet smaller than the dimensions of the vacuum field across the platen surface results in vacuum losses for holding. In other words, too many exposed vacuum ports result in a loss of holding suction and the paper is not firmly adhered to the surface. Generally, known apparatus rely on an end-user manually switching operational functions to adjust the vacuum field to match the size of the paper in current use. The apparatus known in the art also often require a fixed position leading edge registration feature in order to implement various transport vacuum size switching.
There is a need for a vacuum holddown for sheet material transport that can automatically adjust to hold a relatively universal variety of sizes of materials. In a hard copy apparatus implementation, the paper transport system preferably should operate while being moved at a relatively high speed (e.g., for a drum rotating at a surface speed approximately 30-inches/second).
In its basic aspects, the present invention provides vacuum controlled holding apparatus for securing variably sized sheets of flexible material thereon, associated with a vacuum mechanism for generating a vacuum force. The present invention includes: plate mechanisms for sequentially receiving flexible material sheets on a first surface thereof, the plate mechanisms having a plurality of vacuum ports to a second surface thereof, the second surface being subject to the vacuum force; gating mechanisms associated with each of the vacuum ports such that under a first condition, wherein a vacuum port is not covered by a flexible material sheet, the gating mechanisms is closed under influence of the vacuum force and under a second condition, wherein a vacuum port is covered by the flexible material sheet, the gating mechanisms is automatically opened such that the vacuum force is exerted against the flexible material sheet thereby holding the flexible material sheet to the first surface.
In another basic aspect, the present invention provides a method for temporarily securing variably sized, individual sheets of print media to a platen surface using a vacuum mechanisms for generating vacuum force. The method includes the steps of: providing a platen surface with a plurality of discrete vacuum ports therethrough, each of the ports having a gating mechanism for opening and closing the vacuum ports and for segregating the ports into an exterior region and an interior region, wherein the gating mechanism is biased to an open position against atmospheric pressure of the exterior region, and wherein the platen surface has length and width dimensions for sequentially accommodating different sized print media; subjecting each of the vacuum ports to the vacuum force via the interior region, the vacuum force having a predetermined value sufficient for closing the ports with the gating mechanism such that a substantially atmospheric pressure condition exists within the exterior region and a subatmospheric pressure condition exists within the interior region of each of the vacuum ports; and transporting a sheet of print medium onto the platen surface wherein by interaction of the sheet of print medium with the vacuum ports where the print medium is in contact with the platen surface, vacuum ports covered by the sheet of print media have the gating mechanism automatically open due to change in pressure differential between the exterior region and the interior region of the vacuum ports thereby securing the sheet to the platen surface.
In yet another basic aspect, the present invention provides a cut-sheet print medium holddown device for a hard copy apparatus having a mechanism for exerting a vacuum force. The device includes: a platen having a platen top surface having an area sufficient for sequentially accommodating different size sheets thereon, a platen bottom surface, and a field of vacuum ports distributed across the platen coupling the platen top surface and the platen bottom surface; and mechanisms for gating each of the vacuum ports individually wherein sheet coverage of individual vacuum ports causes a pressure differential change across the mechanisms for gating of only sheet-covered vacuum ports, automatically moving the mechanisms for gating associated with sheet-covered vacuum ports from a closed position to an open position such that vacuum force is exerted only through sheet-covered vacuum ports.
In another basic aspect, the present invention provides an ink-jet hard copy apparatus, having a known manner device for producing a vacuum force, where the apparatus includes: printing mechanisms for jetting ink droplets; mounting mechanisms for receiving the printing mechanisms and for selectively positioning the printing mechanisms; and print media holding mechanisms for receiving and capturing a sheet of the media and for transporting a captured sheet to positions within the apparatus where the printing mechanisms is selectively positioned, the print media holding mechanisms including a rotating drum coupled to the device for producing a vacuum force wherein the rotating drum includes a plurality of vacuum ports on an outer surface thereof, mechanisms for manifolding vacuum from a holddown inner surface thereof coupled to the device for producing a vacuum force to the vacuum ports such that the vacuum ports have a first position closing individual the vacuum ports having no region of the sheet present thereon and a second position opening individual vacuum ports having a region of the sheet present thereon.
It is an advantage of the present invention that it provides a vacuum holddown that does not require any change in vacuum for differently dimensioned materials to be held.
It is an advantage of the present invention that it provides an automatic, size compensating, vacuum force distribution method and apparatus.
It is an advantage of the present invention that it provides a vacuum holding surface having reliable vacuum switching.
It is an advantage of the present invention that it provides a vacuum holding surface suitable for use in a hard copy apparatus where the marking subsystem and paper are required to be in close proximity.
It is another advantage of the present invention that it provides a vacuum transport that does not require multi-speed capability, viz. allowing full speed loading and unloading.
It is a further advantage of the present invention that it limits vacuum waste, reducing vacuum power requirements.
It is a further advantage of the present invention that it permits a higher vacuum power, allowing stiffer flexible materials to be transported.
It is still another advantage of the present invention that it eliminates the need for mechanical clamps or fasteners for holding print media.
It is a further advantage of the present invention that it eliminates the need for separate vacuum ON/OFF sensors and switches.
It is yet another advantage of the present invention that it can be adapted to allow multiple sheets of media to be positioned on a platen.
Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.